If using Visual Basic on a course then I'd recommend a native install
of Windows, i.e. full dual boot, as you'll be writing code that may
need direct access to the hardware and the last thing you want is to
have your code not working and it not being the code itself but not
being compatible with a virtual OS ( i.e. running Windows 7 inside
Virtual Box )

If you've already got Ubuntu installed then adding Windows 7 as a dual
boot is messy so your idea of separate HD's is a good one, whether
it's by selecting them on boot or removable drives. What would be a
good idea is to disconnect the Ubuntu drive when installing Windows as
this could cause installation hiccups.